160 The N.Z. Journal of Science and Technology., [Aug, 
favourable for the lactic bacteria that they can outgrow and keep any 
others down. Most bacteria which attack skin thrive only in alkaline 
solutions, and so the slightly acid reaction of the drench affords protection. 
Most of the putrefactive bacteria multiply at a higher temperature than 
that of the bran infusion, and it is thus important to maintain conditions 
of temperature, acidity, and food as favourable as possible for the lactic 
bacteria. 
The bran infusion is usually prepared by mashing the bran in water 
at about 95° F. ; from J to 1 per cent, of bran to the water may be used. 
The pelts are put in and paddled, the temperature of the water falls to 
about 84° F., and the fermentation then commences. No addition of 
bacteria is needed, as sufficient are always present in the paddle-vats. 
The chemical changes taking place in the drenching process appear to 
be that the starch of the bran is first converted into glucose and other 
fermentable sugars by an enzyme naturally present in the bran ; these 
sugars are fermented by the enzymes produced by the bacteria, and con¬ 
verted into lactic and acetic acids, which in turn remove the lime in solu¬ 
tion. The process when proceeding properly appears to be self-regulating, 
because the bacteria, being sensitive to an excess of acid, cease to multiply 
when a concentration of about 0-25 per cent, of mixed acids is reached. 
Consequently until a part of the acids formed is absorbed by the skins the 
production is automatically checked. 
The bran drench for deliming has been superseded in some places by 
the use of commercial lactic and acetic acids of proper strength, while in 
part it has been supplemented by the use in various places of these com¬ 
mercial acids, as well as by the use of hydrochloric and sulphuric acids. 
The purpose, however, is similar—namely, to remove the lime. In connection 
with the use of the bran drench it is of interest to bear in mind that the 
mechanical action of the bran particles in cleansing the surfaces of the pelt 
is of some importance. 
The pelts, after being delimed, are in this country usually preserved by 
a pickling process in order to keep them without putrefaction or injury 
until they can be shipped and worked into leather goods by the purchaser 
in Britain or elsewhere. Pickling consists in treating the pelts with a solu¬ 
tion of common salt and a small quantity of sulphuric acid. In general 
two methods of carrying out the process are in use. The first of these 
methods is that known as a two-bath process. The pelts are first paddled 
in a solution containing about 8 per cent, salt with 0-75 per cent, sulphuric 
acid, this being termed a “ rising solution,” and the skins swell somewhat. 
They are now transferred to a saturated solution of salt, termed a falling 
solution,” and in this they become thin and white. After removal from this 
solution they are ready for packing in casks. The other method, probably 
more commonly carried out in this country, consists in placing the pelt in 
a solution of salt and sulphuric acid, containing about 15 per cent, salt and 
0-75 per cent, sulphuric acid, the pelts being paddled for about an hour in 
this solution. The greater salt concentration prevents tne swelling which 
the sulphuric acid in a more dilute salt solution would bring about in the 
pelt. The pelts when finally pickled contain approximately 12 per cent, 
salt with 0*75 per cent. acid. 
Other acids than sulphuric can be used, and especially formic acid in 
0-25 per cent, solution gives good results when properly used. The pelts 
after pickling by the one-bath process are ready for packing in casks, layers 
of loose crystal salt being added. 
